State switched acoustic transducer

Abstract

A state switched acoustic has a stiffness element having a zero potential energy state and a plurality of controllable stiffness states. A mass is coupled to the stiffness element so that the stiffness element and the mass are capable of resonating at a resonant frequency. A system changes the stiffness state of the stiffness element from a first stiffness state to a second stiffness state while the mass is in motion and stiffness element is in a zero potential energy state so as to change the resonant frequency of the transducer. In a method of changing resonant frequency of a mechanical system, a parameter of the system is dynamically changed while the system is in an energy state that will allow changing the resonance parameter without disrupting the resonance of the system.

What is claimed is: 
     
       1. A variable frequency transducer, comprising: a. a stiffness element having a plurality of controllable stiffness states, the stiffness element including at least one piezoelectric member electrically coupled to a first electrode and a spaced-apart second electrode, the stiffness element being in a first stiffness state when the first electrode is short circuited with respect to the second electrode and being in a second stiffness state when the first electrode and the second electrode are open circuited with respect to each other;   b. a mass coupled to the stiffness element so that the stiffness element and the mass are capable of resonating at a resonant frequency;   c. a circuit that selectively short circuits the first electrode to the second electrode to cause the stiffness element to be in the first stiffness state and open circuits the first electrode from the second electrode to cause the stiffness element to be in the second stiffness state; and   d. means for causing the stiffness element and the mass to vibrate at resonance.   
     
     
       2. The transduce of claim 1, wherein the stiffness element comprises a plurality of piezoelectric members, thereby allowing the stiffness element to have a plurality of stiffness states. 
     
     
       3. The transduce of claim 2, wherein each piezoelectric member comprises a piezoelectric ceramic. 
     
     
       4. The tranducer of claim 3, wherein the piezoelectric ceramic is longitudinally polarized. 
     
     
       5. The tranducer of claim 3, wherein the piezoelectric ceramic is radially polarized. 
     
     
       6. A transducer having a variable resonant frequency, comprising: a. a head mass;   b. a tail mass spaced apart from the head mass;   c. an electrically controlled driver for causing at least one of the head mass and the tail mass to move in resonant motion;   d. a piezoelectric ceramic active spring including a plurality of piezoelectric members, each electrically coupled to a first electrode and a spaced-apart second electrode, each piezoelectric member being in a first stiffness state when the first electrode is short circuited with respect to the second electrode and being in a second stiffness state when the first electrode and the second electrode are open circuited with respect to each other, so that the active spring has a plurality of stiffness states, wherein the resonant frequency of the transducer is a function of the head mass, the tail mass and the stiffness state of the active spring;   e. a circuit that selectively short circuits the first electrode to the second electrode of at least one selected piezoelectric member so as to cause the selected piezoelectric member to be in the first stiffness state and open circuits the first electrode from the second electrode to cause the selected piezoelectric member element to be in the second stiffness state, whereby a combination of the piezoelectric members in the first stiffness state and in the second stiffness state causes the active spring to be in one of the plurality of stiffness states.   
     
     
       7. The transducer of claim 6, wherein each piezoelectric member comprises a longitudinally polarized piezoelectric ceramic. 
     
     
       8. The transduce of claim 6, wherein each piezoelectric member comprises a radially polarized piezoelectric ceramic. 
     
     
       9. A mechanical resonator, comprising: a. a stiffness element having a plurality of controllable stiffness states, the stiffness element including at least one piezoelectric member electrically coupled to a first electrode and a spaced-apart second electrode, the stiffness element being in a first stiffness state when the first electrode is short circuited with respect to the second electrode and being in a second stiffness state when the first electrode and the second electrode are open circuited with respect to each other;   b. a mass coupled to the stiffness element so that the stiffness element and the mass are capable of resonating at a resonant frequency; and   c. a circuit that selectively short circuits the first electrode to the second electrode to cause the stiffness element to be in the first stiffness state and open circuits the first electrode from the second electrode to cause the stiffness element to be in the second stiffness state.   
     
     
       10. The mechanical resonator of claim 9, wherein the stiffness element comprises a plurality of piezoelectric members, thereby allowing the stiffness element to have a plurality of stiffness states. 
     
     
       11. The mechanical resonator of claim 10, wherein each piezoelectric member comprises a piezoelectric ceramic. 
     
     
       12. The mechanical resonator of claim 11, wherein the piezoelectric ceramic is longitudinally polarized. 
     
     
       13. The mechanical resonator of claim 11, wherein the piezoelectric ceramic is radially polarized.